Drop on demand ink jet technology is widely used in the printing industry. Printers using drop on demand ink jet technology can use either thermal ink jet technology or piezoelectric technology. Even though they are more expensive to manufacture than thermal ink jets, piezoelectric ink jets are generally favored, for example because they can use a wider variety of inks.
Piezoelectric ink jet print heads include an array of piezoelectric elements (i.e., transducers or PZTs). One process to form the array can include detachably bonding a blanket piezoelectric layer to a transfer carrier with an adhesive, and dicing the blanket piezoelectric layer to form a plurality of individual piezoelectric elements. A plurality of dicing saw passes can be used to remove all the piezoelectric material between adjacent piezoelectric elements to provide the correct spacing between each piezoelectric element.
Piezoelectric ink jet print heads can typically further include a flexible diaphragm to which the array of piezoelectric elements is attached. When a voltage is applied to a piezoelectric element, typically through electrical connection with an electrode electrically coupled to a power source, the piezoelectric element bends or deflects, causing the diaphragm to flex which expels a quantity of ink from a chamber through a nozzle. The flexing further draws ink into the chamber from a main ink reservoir through an opening to replace the expelled ink.
Increasing the printing resolution of an ink jet printer employing piezoelectric ink jet technology is a goal of design engineers. One way to increase the jet density is to increase the density of the piezoelectric elements.
To attach an array of piezoelectric elements to pads or electrodes of a flexible printed circuit (flex circuit) or to a printed circuit board (PCB), a quantity (e.g., a microdrop) of conductor such as conductive epoxy, conductive paste, or another conductive material is dispensed individually on the top of each piezoelectric element. Electrodes of the flex circuit or PCB are placed in contact with each microdrop to facilitate electrical communication between each piezoelectric element and the electrodes of the flex circuit or PCB.
Achieving reliable electrical connections or interconnects between piezoelectric elements and a circuit layer becomes more challenging at increasing print head resolutions. Design constraints that require dimensionally smaller PZTs reduce both the surface area available for forming an electrical interconnect as well as the area for its surrounding bond adhesive. For example, openings within a standoff layer for an electrical connection between the circuit layer and PZT can be decreased by more than 60% across an array having 600 dots per inch (dpi) compared to an array having 300 dpi. Similarly, an effective bonding area can be reduced by more than 40% across an array having 600 dpi compared to an array having 300 dpi. This reduction in bond area can result in weaker electrical interconnects that may fail after stressing due, for example, to thermal cycling, thermal aging, and PZT actuations.